Propylene polymers are thermoplastic and hence can be melted by heating and molded to give articles having various shapes. Therefore, the propylene polymers are widely employed, for instance, for producing sheathing parts of automobiles, housings of household electric appliances such as refrigerators and washing machines, and other various molded products such as trays, shelf plates and wrapping films. It is known that the propylene polymers are mixed with additives such as inorganic fillers, lubricants and elastomers so as to improve rigidity and impact strength of the molded products. As the inorganic fillers, there are known fibrous inorganic fillers such as a fibrous basic magnesium sulfate filler and non-fibrous fillers such as talc. Basic magnesium sulfate has the chemical formula of MgSO4.5Mg(OH)2.3H2O.
JP 2006-83369A (corresponding to U.S. 2006/0052544A1) describes a method for producing a propylene-based resin composition comprising a first step of producing a first resin composition (MB) by melt-kneading a first-propylene polymer (A-I) and a fibrous inorganic filler (B) in a weight ratio of (A-I) to (B) of from 3/7 to 7/3; and a second step of producing a second resin composition by adding a second propylene polymer (A-II), a non-fibrous inorganic filler (C) and an elastomer (D) selected from the group consisting of olefin-based elastomer and vinyl aromatic compound-containing elastomer to the first resin composition (MB), followed by melt kneading them. In the working examples, the first resin composition (i.e., master batch composition) contains a lubricant.
There are cases in which molded products made from an olefin polymer composition are desired to show further increased impact strength. For instance, bumpers and other sheathing parts of automobiles for driving at low temperatures are desired to show high impact strengths such as high izod impact strength and surface impact strength at low temperatures such as lower than 0° C., keeping the high modulus in flexure.